Spark-plug.



W. STEVENSON.

SPARK PLUG.

APPLICATIQN FILED JAN. 11.1911.

1,250,242. Patented Dec. 18,1917.

WITNESS ATTORNEY.

Enron.

WILLIAM STEVENSON, 0F MORRISTOWN, NEW JERSEY.

SPARK-PLUG.

Specification of Letters Patent.

Patented nee, is, Tea to Application filed January 11, 1917. Serial No. 141,776.

To all whom it may concern:

Be it known that I, WILLIAM STEVENSON, a citizen of the United States, residing at- Morristown, in the county of Morris and State of New Jersey, have invented certain new and useful Improvements in Spark- Plugs, of which the following is a specification.

This invention relates to terminal devices, and it has for its principal object to provide a terminal device of the spark plug typewhich shall be greatly superior in point of strength, durability and simplicity of construction to ordinary spark plugs of the class embodying a more or lesssizable body of frangible insulating material, such as porcelain, and which nevertheless shall be quite as efficient as ordinary spark plugs, for instance in respect to immunity to shortcircuiting.

My invention distinguishes from other terminal devices mainly in this, that it embodies insulation of rolled-up sheet material separating the terminal member which forms the metallic body of the device from the other terminal member, the two members so coacting with respect to the rolled-up sheet material as to close up interstices be,- tween the layers thereof in such a way as to prevent all possibility of short-circuiting, as by the interposition of oil or other fluid between said layers. For the sheet material, T preferably employ mica. My inven tion distinguishes from other terminal devices in certain other respects which will be set forth in detail in the following specification and finally embodied in the clauses of the claim.

in the accompanying drawing,

Figure l is a side elevation of the improved spark plug;

Fig. 2 is a vertical sectional view thereof, showing the inner or stem terminal member in elevation; and

Figs. 3 and 4 are perspective views of the two portions I prefer to use for the sheet insulating material, Fig. 4 also showing the inner terminal member.

The outer terminal member, which forms the body of the device, consists of a tubular metal pillar a having a screw-threaded extension 5 at its lower end whereby it may be screwed into the engine cylinder 01' other support and also having a faceted portion 0 to receive a wrench. The bore d of said pillar tapers upwardly, as clearly shown in Fig. 2.

The inner terminal member is a stem 6 also tapering upwardly at preferably the same pitch as the taper of the bore 03, being of somewhat less diameter than said bore. At its upper end said stem is provided with a threaded extension f.

The terminal members a and e have the terminals proper a and e projecting from their lower ends and into such proximity to each other as to form the desired spark-gap.

Spirally rolled up insulating sheet material, preferably sheet mica, is interposed between said members a and e, the latter .of which penetrates the former and coacts therewith to hold the said rolled-up insulation in a state of compression, due to member 6 standing in wedged-in relation to member a and the interposed insulation. The insulation is preferably in two telescoped sections or rolls 9 and h, each of rolled-up sheet material rolled so as to possess a taper of the same pitch as that of the bore (i of member c. Having formed the section 9', it is inserted in said bore d, which it snugly fits, standing with its ends flush with the ends of member a. Having formed the section h it is inserted in section g, but preferably stands with its upper and lower ends elevated above the corresponding ends of the section 9'. The stem is then inserted into section it and driven home, leaving the layers of insulation so compacted as to close up any interstices between them likely to admit oil or other fluid that might lead to a shortcircuit. When the stem is fully home, its upper end preferably stands about flush with the upper end of section 7a of the insulation, but its lower endprotrudes somewhat to receive the blow of the driving tool. A plurality of rolls (9 and h) are employed because I find that T can thereby attain greater compactness and hence greaterassurance of perfect insulation when the memher 6 is driven home than T can with a single piece of the material, obviously because each section is free to slip somewhat within the other; moreover, the compacting is more uniform and the wedging-inof member e is accompanied with less tendency to produce an undesirable prolongation of the spiral axially.

The upper or free end of the device is constructed tor the attachment of the condition Venting any possibility ing wire to the stem member 6 and for preof short-circuiting at this point, the means devised to this end acting also to maintain the stem member. in its wedged-in relation. That is to say: A stout nut i is screwed onto the threaded extension f of the stem member and obtains thrust or bearin on a cap or crown j which includes a cylindrical portion 9'', snugly fitting the protruding upper end of the insulation section it and seated upon the upper ends of the member a and insulation section 9, and a concavo-convex flange j at the top of portion j and having its convex side up.

This cap or crown is composed of insulating material, preferably some hard, tough substance of a substantially infrangible nature, as bakelite. Any possibility of short-circuiting from stem member 6 to body member a within the cap or crown is prevented by the tight fit of the latter to the protruding portion of insulation section hand by-the cap or crown being tightly held abutting squarely against the upper end of insulation section g, taken with the fact that the gap between the stem and body members is made in efi'ect considerable by extending the insulation section it above the top of member a. Any possibility of short-circuiting from nut a to member a exteriorly is prevented by the vertical height of the insulating cap or crown plus the distance to the periphery of its flange and back afiording a gap too great for the current to cross. The upper side of the cap or crown being convex any liquid falling thereon will run 0%.

Short-circuiting at the lower end of the device is prevented by the stem-member 6 being elevated reference to the lower end or the insulation in body member a and with 1.v A terminal device including terminal members, one penetrating the other, and a tubular body of insulating material arranged in telescopcd relation to said members and including a plurality of separate spiral rolls of sheet material telescoped one in the other, the penetrating member being held wedgefashion in said body and thereby coacting with the penetrated member to maintain said body circumferentially compressed between them.

2. A terminal device including an outer terminal member having a terminal proper at one end thereof, a tubular insulating section penetrating said member and. reaching approximately to the terminalproper-end thereof, another tubular insulating section penetrating the first tubular insulating section and extending short of said end of said member but protruding from the relatively opposite end of the first section, an inner terminal member penetrating the second insulating section and coacting with the first member to hold said sections pressed wedge-fashion between them, and means, including an insulating device fitted over said protruding end of the second insulating section, for holding the inner terminal member in place.

In testimony whereof ll aiiix my signature.

WILLIAM STEVENSUN. 

